Exhaust systems including exhaust hoods are used in many industries to remove polluted air from a work area. This may include the manufacturing and chemical industries. In particular, they are used in kitchens such as industrial and commercial kitchens in the food processing industry, and restaurants of all types and categories. In commercial kitchens food is quite often cooked in oil, or by using oil as a lubricant. The cooking fumes contain oil droplets. Filters include a stainless steel mesh to capture the majority of oil droplets and may be located in the exhaust hood, the flue of the exhaust hood, or in the ducting. Droplets not captured by the filter land on the surface of the exhaust hood, the flue, the ducting, or are exhausted to atmosphere. When the oil droplets cool and start to dry they become very sticky, and are hard to remove. Also, such filters have a fairly open mesh as if a fine mesh is used they can become clogged (and thus become ineffective) very quickly. The exhaust hood can also be quickly lined with the cooled and dried oil, as can the flue and the ducting. This leads to many problems: a rapid build-up of bacteria in the cooled and dried oil—a major problem in a commercial kitchen; and increased fire risk from the oil; ineffective exhaust operation leading to greater workplace health and safety issues; and increased pollution of the atmosphere.
Cleaning exhaust hoods and the filters manually is time-consuming, tedious, and labour intensive task. Also, some of the flue and/or ducting may be inaccessible for cleaning.
There have been many proposals for self-cleaning using water curtains, water baths, or sprays. Most have the problem that they cannot be operated during cooking process—when the oil is most fluid and therefore more easily removed. Most do not improve the elimination of oil from the exhaust air to atmosphere.